Boško Rašuo

Numerical Simulation of Air Jet Attachment to Convex Walls and Application to UAV

In this paper, we present a numerical study of the wall jet flow over a convex surface, viz. the Coanda wall jet, and its application to a conceptual Unmanned Aerial Vehicle (UAV) design which uses the Coanda effect as a basis of lift production. This configuration is important in a way that it considers the Coanda wall jet over a smooth convex wall with non-constant curvature, in contrast to most of the previous situations where only constant curvature walls were considered e.g. the Coanda wall jet over circular cylinder. To enable the mathematical representation of this complex geometrical configuration, we propose a form of a parametric representation of the conceptual geometry, based on Bernstein polynomials, which is universal in character and spans a complete design space. It is shown how dynamically changing the flow picture enables smooth change of net forces on the body. Capability to control the direction of the net force is shown to be useful for maneuvering the UAV. All simulations are done using an open-source finite-volume computational fluid dynamics code based on Reynolds-averaged Navier-Stokes equations. Turbulence is accounted for using the k −ω Shear Stress Transport model.

Experimental Techniques for Evaluation of Fatigue Characteristics of Laminated Constructions from Composite Materials: Full-Scale Testing of the Helicopter Rotor Blades

The importance of full-scale testing in the development process for composite laminated materials helicopter blades is discussed and illustrated by means of two examples drawn from the Aeronautical Department, Faculty of Mechanical Engineering’s experience in the use of composites in a wide variety of structural applications. Laboratory fatigue testing is conducted at the Aeronautical Department on all flight-critical dynamic components in order to determine structural adequacy. In this paper, the analyses of behavior by fatigue testing for a main rotor blade for a light multipurpose helicopter propulsion system and a heavy transport helicopter tail rotor blade of composite laminated materials are given. The blades were fabricated from composite laminated materials. The contour of airfoil was formed by a continuous structural pocket, which had a Rohacell foam core and a fiberglass skin. The upper and lower skins were fabricated from woven fiberglass that was laid up with fibers oriented at 45° and 0°/90° to the blade’s longitudinal axis. In the trailing edge of both skins, graphite fibers were placed for stiffening. Fatigue testing of the helicopter blades was accomplished in a special test facility designed to simulate the inflight loading. The applied test loads include simulated steady centrifugal, vibratory chordwise bending, vibratory flapwise bending, and vibratory torsional pitch motion. The fatigue analyses of these composite laminated structures were performed after fatigue test cycles for the detection of laminate separation, tolerance, and distortion of structure cross sections.

T-38 Wind-Tunnel Data Quality Assurance Based on Testing of a Standard Model

The tests of the standard models serve to confirm the overall accuracy and repeatability of measurements in every single wind-tunnel facility and to confirm confidence in results obtained. The intention of the authors in this paper is to present, with exemplary test results, a methodology for certification and verification of the overall reliability of the T-38 Military Technical Institute’s trisonic wind tunnel on the basis of check standard testing together with a small number of repeat-run sets prior to the customer’s tests. Wind-tunnel data uncertainty is considered in the form of repeatability of a few presumably identical tests of a standard model. Test data are also correlated with those from other wind-tunnel facilities.

On the improved finite volume procedure for simulation of turbulent flows over real complex terrains

This article presents a new and substantially improved finite volume procedure for simulation of incompressible flows on non-orthogonal grids. Cell-centered least-squares gradients are obtained in a robust and highly accurate way. A new discretization of the diffusive terms is employed, which is based on extension of the original cell-face gradient interpolation and is more suitable for complex grid distortions. A flexible flux-limited interpolation of dependent variables on distorted computational grids is introduced. An efficient preconditioner for Krylov method solution of linear systems is proposed, which substantially improves the solution of Poisson equation for pressure correction. The pressure-correction algorithm is adapted for efficient convergence on highly complex grids using a sequence of non-orthogonal corrector solutions and its effect on iteration convergence is analyzed. The non-orthogonalities treated by current procedure are more accustomed to numerical grids generated from a real complex terrain elevation data. The main focus is on the simulation of atmospheric micro-scale flows pertinent to wind energy application.

Some Analytical and Numerical Solutions for the Safe Turn Manoeuvres of Agricultural Aircraft - an Overview

In this paper, a theoretical study of the turn manoeuvre of an agricultural aircraft is presented. The manoeuvre with changeable altitude is analyzed, together with the, effect of the load factors on the turn manoeuvre characteristics during the field-treating flights. The mathematical model used describes the procedure for the correct climb and descent turn manoeuvre. For a typical agricultural aircraft, the numerical results and limitations of the climb, horizontal and descending turn manoeuvre are given. The problem of turning flight with changeable altitude is described by the system of differential equations which describe the influence of the normal and tangential load factors on velocity, the path angle in the vertical plane and the rate of turn, as a function of the bank angle during turning flight. The system of differential equations of motion was solved on a personal computer with the Runge-Kutta-Merson numerical method. Some analytical and numerical results of this calculation are presented in this paper.

Minimal safe speed of the asymmetrically loaded combat airplane

Purpose – The purpose of this paper is to present a method for determining the safe flight boundaries of the asymmetrically loaded airplane in the terminal flight phases. The method is applicable to both, the inherent airplane asymmetries and those asymmetries resulting from the airplane use irregularities, asymmetric stores under the wing being one of the examples. The method is aimed to be used in the airplane design and combat airplane service life support. Design/methodology/approach – The analysis method is based on the comparison of demanded and structurally available flight control displacements. Control surface aerodynamic properties, structurally available flight control displacements and dynamic pressure define control surface authority as the capability of control surfaces to generate the forces and moments needed by the airplane to perform required maneuvers. Demanded flight control displacements are those related to the maneuvering requirements and to those needed to compensate lateral wind a...

Optimization of the aircraft general overhaul process

Purpose – The purpose of this paper is to present the development results of the overhaul melioration plan for the following aircraft types: MiG‐21Bis, G‐4 Galeb and SA‐341 helicopter. This research has been conducted based on available knowledge and extensive experience gained by performing general maintenance of the Air Force of Serbia aircraft.Design/methodology/approach – A general analysis was performed by processing data collected while performing maintenance and repair procedures. The magnitude of data is based on detecting the delays and errors that occurred while going through the operational and inter‐operational stages of aircraft overhaul. On the basis of the obtained research results, a proposal for the aircraft overhaul optimization is offered.Findings – The proposed overhaul improvement plan points out the priority steps to be taken in order to optimize the most critical features that jeopardize the quality of the aircraft overhaul process relating to organization, technology and design. Mo...

On-Condition Maintenance for Nonmodular Jet Engines : An Experience

Using updated knowledge and gained experience in engine control and maintenance, a specific on-condition maintenance concept of RD-33 engines installed on MiG-29s was developed. The engines had several built-in limitations: number of starts, number of hours at the maximum power and reheat, number of hours at the special regime of elevated temperatures, and time between overhauls (TBOs), that is, number of flight hours. During field data collection and analysis, it was found that engines worked with different working loads and different levels of life consumption. Hence, it was concluded that the limitation of TBO, expressed in terms of flight hours, do not represent actual engine health condition and that a new way of monitoring actual load needs to be introduced. An analysis of all flight profiles was carried out and a specific relation between flight hours and total accumulated cycles (TACs) was established. For this purpose, a distributed expert system in relation-operation unit-Air Force Technical Institute-overhaul depot was introduced. Each of the three participants has its own level of responsibility in the engine health monitoring, engine maintenance, and engine health condition decision-making process. Nondestructive inspection, remote visual inspection, spectral oil analysis, fault tolerant control techniques of hot engine parts, engine electronic control unit, airplane information-display system, engine performance trend monitoring, vibration monitoring, and postflight data analysis play key roles in the concept. It has been applied in practice since 1994; all faults were discovered right in time, and there were not any critical situations in flight. Detected faults were isolated and assessed for severity, so that the remaining useful life could be estimated. The original TBO was safely extended on the basis of TAC of up to more than 50% of the originally prescribed TBO hours, while maintaining the same safe margin.

Verification Testing of Aeronautical Constructions from Composite Laminated Materials in Designing Process

The importance of verification testing in the design process for composite laminated materials aeronautical constructions is discussed, and illustrated by means of two examples drawn from Aeronautical Department (Faculty of Mechanical Engineering, University of Belgrade) experience in the use of composites in a wide variety of structural applications. Laboratory verification testing is conducted at Aeronautical Department on all flight-critical dynamic components in order to determine structural adequacy. In this paper the analysis of behavior by verification testing for a main rotor blade for a light multipurpose helicopter propulsion system and a heavy transport helicopter tail rotor blade of composite laminated materials are given.

An Evaluation of the Overall T-38 Wind Tunnel Data Quality in Testing of a Calibration Model

Tests of standard models serve to confirm the overall accuracy and repeatability of measurements in a wind tunnel facility and to confirm confidence in results obtained. The intention of the authors in this paper is to certify and to verify the overall reliability of the VTI’s trisonic wind tunnel. The methodology is based on the check standard testing. Wind tunnel data uncertainty is considered in the form of repeatability of a few supposedly identical tests of a standard model. Test data are also validated based on comparisons with those from other wind tunnel facilities.